The invention relates to methods for measuring the remaining useful life of a filter during flow of a particulate-laden fluid through the filter.
As a particulate-laden fluid passes through a filter, the particulates are retained in the filter. It is generally desirable to change or clean a filter element of the filter before it becomes completely blocked with particulates as further clogging could lead to excessive differential pressures within the filter. The point at which such a change or cleaning is desirable is called the end of the useful life of the filter.
One known method of indicating the end of the useful life of a filter measures the differential pressure of the fluid across the filter as fluid is passed through the filter and particulates are retained by the filter. As the amount of retained particulates increases, the differential pressure increases and, by previous testing, a differential pressure can be determined at which the filter is at the end of its useful life.
A known device detects the differential pressure across the filter and gives an alarm signal when the previously determined differential pressure is reached. This apparatus provides no indication of the rate at which the filter is retaining the particulates and thus no indication of the remaining useful life and does not allow prediction of when the filter will have to be replaced or cleaned.
Another known device also detects the differential pressure of the fluid across the filter and provides a rough indication of the differential pressure using a light emitting diode bar-graph. The number of diodes that are illuminated increases roughly in linear proportion to the increases in differential pressure. This apparatus does not readily allow a prediction of when it will be necessary to replace or clean the filter, because the changes in differential pressure are not linearly related to the changes in the remaining useful life of the filter.
According to an aspect of the invention, there is provided a method of measuring remaining useful life of a filter comprising flowing a particulate-laden fluid through the filter, measuring a parameter of the flow during the flowing, and producing, from the measurements of the parameter, measurements of the remaining usefull life of the filter that vary linearly during the time in which the fluid is flowing through the filter, including storing in a store a previously measured correlation between the parameter and remaining life for a trial filter corresponding to the filter on flowing the particulate-laden fluid therethrough, the store receiving the measurements of the parameter and outputting measurements of the remaining useful life corresponding to the received measurements of the parameter and derived from the previously measured correlation.